It has been shown that the visual system is subject to sensory attenuation (Cardoso-Leite, Mamassian, Schutz-Bosbach, & Waszak, 2010). This phenomenon is thought to be related to motor based sensory prediction. In this study we first develop a model to account for how this prediction might be implemented in the brain. This model supposes that the voluntary action selection involves the preactivation of learnt action-effects (Waszak, Cardodo-Leite, Hughes, 2011). By modeling motor induced preactivation in sensory pathways we predict that sensory attenuation is due to a nonlinear increase of the internal response. One novel prediction of this model is that it should result in a change of contrast discrimination sensitivity for correctly predicted action effects. We tested this hypothesis by conducting a contrast discrimination task for visual stimuli that were either congruent or incongruent with previously learnt action-effect contingencies. Participants freely selected on each trial which of two buttons to press (one with each index finger). Each button press was followed, with a delay of 200ms, by the presentation of either an A or an H, at one of two contrast levels (C0 and C1, individually determined to produce a contrast discrimination sensitivity d’ of 2). On each trial, participants were required to report the perceived contrast of the visual stimulus. We observed a significantly (F(1,11) = 5.59, p <0.05) reduced contrast sensitivity for trials where the stimulus was congruent (M=1.82 SEM=0.56) with the learnt action-effect contingency, compared to when it was incongruent (M=1.98 SEM=0.61). Hence the prediction made by our preactivation model was confirmed and provides a new way to consider how the brain predicts the sensory consequencies of the action.